1. Field of the Invention
This invention relates to novel polymeric peroxides used as a free radical polymerization initiator for vinyl monomers and having two peroxy groups of different thermal decomposition rates.
2. Related Art Statement
As a polymeric peroxide having two or more peroxy groups in one molecule, there have hitherto been known peroxides in which these peroxy groups have the same thermal decomposition rate, and peroxides in which the peroxy groups have different thermal decomposition rates. As the former polymeric peroxide, there are reported a diacyl-type polymeric peroxide obtained by reaction between phthalic chloride and sodium peroxide in Berichte der Deutschen Chemischen Gesellschaft (Ber.), vol. 27, page 1510 (1984), a diacyl-type polymeric peroxide obtained by reaction between oxalic chloride and sodium peroxide in Journal of the American Chemical Society (J. Am. Chem. Soc.), vol 68, page 534 (1946), and diacyl-type polymeric peroxides of the following general formula: ##STR1## (wherein n is 2-10 and x is 16-35) obtained by reaction between a chloride of aliphatic dibasic acid and sodium peroxide in Chemical Abstracts (Chem. Abst.), vol. 60, 5293d and 10892e (1964).
As the latter polymeric peroxide, there are reported polymeric peroxide obtained by reaction between a substituted succinic acid and p-diisopropyl benzene dihydroperoxide in Journal of Organic Chemistry in USSR (J. Org. Chem. USSR), vol. 13, No. 1, page 210 (1977), and polymeric peroxide obtained by alternately bonding the following groups: ##STR2## (where X is --CH.sub.2 CH.sub.2 -- group or --C.tbd.C-- group) in Japanese Patent laid open No. 59-8727.
As mentioned above, there are known several polymeric peroxides, among which the known ester-type polymeric peroxides having different thermal decomposition rates contain primary acyl group ##STR3## and secondary acyl group ##STR4## Therefore, when such a polymeric peroxide is used as a polymerization initiator, it is decomposed at one stage and the polymerization temperature is restricted to a range of 50.degree. C. to 130.degree. C. On the other hand, there is known no polymeric peroxide as an initiator decomposed at two stages and used at a polymerization temperature of 40.degree.-90.degree. C. However, it may be desired to decompose two kinds of peroxy bonds in the polymeric peroxide at a relatively low temperature in accordance with the monomer to be polymerized. Recently, it is strongly demanded to develop polymeric peroxides satisfying such a requirement.